Nitrate spike?

[jock-o]

Up until today my water quality has been good for my area. Ph- 7.2, nitrites- 0-ppm, ammonia- 0-ppm, nitrates 10-ppm. I just finished testing my water and everything was good except nitrates which were 40ppm. The only thing I've change was that when I did a water change last night I trimmed back my Amazon Swords, and I reduce the flow from my w/dry filter mag 7 which was really keeping my tank churning. What will cause nitrate spikes. I could be over feeding, I've been feeding medicated food due to a problem and I want to make sure all the fish are getting it.
Thanks for any info
John

[KDodds]

Are you in a rural area? If so, check your tap. With Spring coming, a lot of localities see phosphate and nitrogen run-off from pre-spring ferilization in preparation for the planting season.